50: Pulmonary Circulation Flashcards
What is the total blood volume in pulmonary vasculature?
600 ml supine falls by 20%
on standing
What happens to blood volume during forced inspiration?
allows an increase to ~1
liter by reducing intrathoracic pressure – opening vessels up
What happens to blood volume during forced expiration?
reduces volume to ~300
ml by raising intrathoracic pressure
What is the blood volume in pulmonary capillaries at
any 1 instant?
100 mL
What happens to blood volume during heavy exercise?
increase from 100 to 150 mL
Increased cross sectional area (and higher resident volume) helps to slow blood down where?
Capillaries
Systemic arteries/arterioles
thick and have a lot of smooth muscle
divert blood flow to places with max requirements
Pulmonary arteries
little smooth muscle and thin walls (very compliant)
Pulmonary capillary
walls are very very thin
Why are Pulmonary
Pressures so Low?
high pressures would cause blood to drain into lungs
Threshold for edema?
25 mm Hg
Hydrostatic pressure is high
enough to push fluid out of
blood into alveoli
How much of the cardiac output does the lung receive?
receives 100% of CO
5L at rest
20L during exercise
How much pressure drives flow in the systemic vasculature?
100 mm Hg
100 mm Hg/ 5L = 20 units
How much pressure drives flow in the pulmonary circuit?
7 mm Hg
7 mm Hg/ 5L = 1.4 units
Pulmonary Vascular Resistance
decreases as cardiac output increases
more blood pumped out, pulmonary arterial pressure increases, pulmonary vascular resistance decreases
Pulmonary Arterial Pressure
minimal increase during exercise to avoid edema
5 mm Hg increase in
pressure results in 4x the flow b/c of increase CO
Recruitment
use of already available cross sectional area
Distention
vasodilation can open up new cross sectional area to further
augment total cross sectional area
Extra-alveolar vessels
larger and
have a web of interlinking
alveolar vessels between them in
parallel
What is the alveolar vessels response to change in lung volume?
Alveolar vessels in walls of alveoli
vessels pulled closed as alveoli expand
resistance increases as the lung inflates
like stretching rubber band
What is the extra-alveolar vessels response to change in lung volume?
sensitive to
radial traction (high
transpulmonary pressures) and pull open as alveoli expand
resistance decreases as the lung inflates
Forces promoting fluid filtration
↑capillary hydrostatic pressure ↓colloid oncotic pressure ↑surface tension ↓lymphatic drainage ↑ capillary permeability
Forces promoting fluid absorption
↑ colloid oncotic pressure
↑ air pressure
↓ capillary hydrostatic pressure
Regional hypoxia
promotes vasoconstriction
less blood to that area of the lung
Global hypoxia
all capillary beds and lungs vasoconstrict b/c low oxygen
can cause high altitude pulmonary edema
Nifedipine
calcium channel blocker
prevents high altitude pulmonary edema
Where does most ventilation of the lung go?
Base of lung b/c of gravity
Where does least ventilation of the lung go?
Apex of lung
Which side of heart is low pressure pump?
Right heart
Low or No Ventilation
leads to shunt
venous blood has gas exchange at alveoli and comes back to left heart deoxygenated
Pulmonary Capillary Wedge Pressure (PCWP)
cardiac catheterization to read left atrial pressures
Used to determine degree of congestion in
pulmonary circuit
Heart failure & pulmonary congestion : increased PCWP
Increasing Shunt
administering oxygen does not change blood oxygen levels
leads to hypoxemia (low oxygen in blood)
Lung Zoning
Zone 3: arterial and venous pressure must exceed alveolar pressure so no compression along length of vessel
